1. Field of the Invention
The present invention relates generally to a semiconductor device, and more particularly, to a semiconductor device having a high voltage generator with a short pumping operation time and improved efficiency in current usage. A claim of priority is made to Korean Patent Application No. 03-78641 filed on Nov. 7, 2003 in the Korean Intellectual Property Office, the disclosure of which is hereby incorporated by reference in its entirety.
2. Description of the Related Art
It is quite common for a semiconductor device to use a relatively higher voltage to drive some circuits as compared with other circuits internal to the device. For example, a semiconductor memory device will often use a voltage to drive word lines that is higher than a normally provided external voltage. The term “external” generally refers to a voltage provided by a circuit outside the semiconductor device itself, as compared with “internal” voltages which are generated by circuits within the semiconductor device. Thus, where a relatively higher voltage is required, the semiconductor device typically includes a high voltage generation circuit that converts the external voltage supplied to the semiconductor device into a signal suitable for use by high voltage circuits and components. In conventional semiconductor devices, a pumping circuit is generally used as a high voltage generation circuit.
In situations where a host system runs off of ordinary batteries, similarly constructed, high voltage generation circuits are typically required to internally generate voltages exceeding the nominal output of the batteries.
Recent host system evolutions have consistently seen power source voltages decreased. As a result, the externally provided power source voltages applied to semiconductor memory devices within the host systems has also been decreasing. While some accommodation to lower externally supplied voltages has been made within the design of semiconductor memory devices, the amount by which the internally required high voltages can be reduced is proportionally much less than the amount by which the external power source voltage has been reduced. Accordingly, it is increasingly difficult to generate the required high voltages with semiconductor memory devices using conventional high voltage generators.
In addition to the problem of unmet overall demand for high voltages, the relative pumping efficiency of high voltage generators is also becoming a problem. That is, as externally supplied voltages have decreases, the pumping efficiency of conventional circuits generating high voltages has markedly dropped.
Further problems arise from the decrease in externally supplied voltages. Fir example, conventional high voltage generation circuits typically require the use of one or more pumping circuits that use capacitors. When the externally supplied voltage is significantly lower than a desired high voltage, it is not uncommon to see three or more boosting stages used to develop the high voltage. Unfortunately, the time required to fully pre-charge the capacitors in each of these boosting stages increases proportionally, and as a result, the time for one operation increases to the point where the entire boosting timing becomes unacceptably long.